Wireless charging circuit, wireless charging system and semiconductor device

ABSTRACT

To satisfy the NFC communication standard in wireless charging with a shared antenna, used for NFC communication. A power supply unit includes a voltage step-down circuit  331 , a charge control circuit  332 , and a communication controller power supply circuit  333 . The voltage step-down circuit includes a switching regulator  200 , and a selection circuit  206  and  208  which can select an output path PT 1  of the switching regulator and a bypass path PT 2  of the switching regulator. The voltage step-down circuit includes a selection control circuit  207 . The selection control circuit supplies voltage to the communication controller power supply circuit via the bypass path at the time of activating the communication controller. Since the output voltage of the series regulator stabilizes in a shorter time than the switching regulator, it becomes possible to keep the time from when RF power rises to when initial communication becomes possible, within standards.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/782,009, filed Mar. 1, 2013, which claims benefit of priority fromthe prior Japanese Application No. 2012-054509, filed Mar. 12, 2012; theentire contents of all of which are incorporated herein by reference.

BACKGROUND

The present invention relates to wireless power feeding technology forwirelessly supplying power from the transmission side to the receivingside, and is particularly and preferably applicable to a wirelesscharging circuit and a wireless charging system, used for charging abattery by wireless power feeding, and a semiconductor device usedtherefor.

Patent document 1 (Japanese Patent Laid-Open No. 2003-141484) describesa non-contact/contact IC card which can transmit and receive signals viaa non-contact interface even if sufficient power supply is not obtainedin a non-contact manner. Particularly, paragraph 0016 of the PatentDocument 1 describes a configuration for performing power feeding andcommunication in a non-contact manner.

In addition, NFC (Near Field Communication) can be exemplified asnon-contact communication technology. NFC, an international standard oflow power wireless communication technology for a distance of about tencentimeters, is being incorporated in small mobile terminals such assmart phones. In contrast, a technique referred to as wireless chargingcapable of non-contact (also referred to as “wireless”) power supply isbeing on the rise, and a group named WPC (Wireless Power Consortium) hasentered the market with expectation of promoting the contactlesscharging standard (Qi).

Patent Document 2 (Japanese Patent Laid-Open No. 2009-253649) describes,a technique of controlling the operation of an information transmissionmeans of performing wireless information transmission and a powertransmission means of performing non-contact power transmission, betweencommunication devices having the information transmission means and thepower transmission means.

SUMMARY

13.56 MHz is used as the carrier frequency in NFC, and the range of 100to 200 kHz is used as the carrier frequency for wireless charging whichis the mainstream of the electromagnetic induction method. Accordingly,NFC and wireless charging of the contactless charging standardrespectively require dedicated antennas because they have mutuallydifferent carrier frequencies, and thus it becomes difficult to securelocations for installing antennas for small mobile terminals such assmart phones. Therefore, wireless charging with a shared antenna, usedfor NFC communication is under consideration.

Since the voltage supplied in a wireless manner is as high as 100 to 200V at the antenna end, and is still as high as several dozen volts evenafter passing through a matching circuit or a rectifier circuit, a lossequivalent to the voltage difference may occur within the IC (IntegratedCircuit) when attempting to charge a single cell of battery (4 to 4.2 V)upon receiving the voltage. As a measure to solve the above-mentionedproblem, it is conceivable to provide a switching regulator (DC-DCconverter) which converts a direct voltage into another direct voltage.That is, the switching regulator lowers the voltage, to input anappropriate voltage to the charge control circuit. Since there is lesspower loss with the switching regulator, loss in the IC can be reduced.

In wireless charging, initial communication is required for exchanginginformation before charging such as whether or not the target ofcharging is an authenticated device, or information about link status orabout required power for charging. Since the initial communication isthe wireless charging with a shared antenna, used for NFC communication,it is natural to perform the communication on the basis of the protocolof NFC communication. According to the NFC communication standard onthis occasion, it is required to keep the time from when RF (RadioFrequency) power rises to when the initial communication becomespossible, for example, 5 ms or less.

However, it takes a while for the switching regulator to stabilize theoutput voltage, and thus letting the switching regulator perform powersupply to the microcomputer for controlling NFC communication makes itextremely difficult to achieve the requirement of keeping the time fromwhen RF power rises to when the communication becomes possible, 5 ms orless.

The other purposes and the new feature of the present invention willbecome clear from the description of the present specification and theaccompanying drawings.

The following explains briefly the outline of a typical invention amongthe inventions disclosed in the present application.

That is, a wireless charging circuit includes a coil antenna, acommunication controller, a rectifier circuit, and a power supply unit,the power supply unit including a voltage step-down circuit, a chargecontrol circuit, and a communication controller power supply circuit.The voltage step-down circuit includes a switching regulator which canreduce the voltage output from the rectifier circuit, and a selectioncircuit which can select an output path of the switching regulator and abypass path for bypassing the switching regulator. Furthermore, thevoltage step-down circuit includes a selection control circuit. Theselection control circuit causes the selection circuit to select thebypass path at the time of activating the communication controller, tothereby supply voltage to the communication controller power supplycircuit via the bypass path. Then, the selection control circuit thencauses the selection circuit to select an output path of the switchingregulator after the output voltage of the switching regulator hasreached a predetermined level, to thereby supply the output of theswitching regulator to the communication controller power supplycircuit.

The following explains briefly the effect acquired by the typicalinvention among the inventions disclosed in the present application.

That is, a technique for satisfying the NFC communication standard canbe provided in wireless charging with a shared antenna, used for NFCcommunication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary block diagram showing an overall configuration ofa wireless charging system;

FIG. 2 is an exemplary block diagram showing a power supply unit in thewireless charging system shown in FIG. 1;

FIG. 3 is an exemplary circuit diagram showing a configuration of aswitching regulator;

FIG. 4 is an exemplary circuit diagram showing a configuration of aseries regulator;

FIG. 5 is a timing diagram from when RF power rises to when initialcommunication becomes possible;

FIG. 6 is an exemplary circuit diagram showing a configuration of aselection control circuit; and

FIG. 7 is an operation timing diagram in the selection control circuitshown in FIG. 6.

DETAILED DESCRIPTION

1. Outline of Embodiments

The following explains briefly the outline of typical embodimentsdisclosed in the present application.

Reference numerals in the drawings, parenthesized in the outlinedexplanation of the representative embodiments, only exemplify what isincluded in the concept of components to which they are provided.

[1] A wireless charging circuit (3) according to a representativeembodiment includes a coil antenna (36), a communication controller (35)which can control short distance wireless communication performed viathe coil antenna, a rectifier circuit (32) for rectifyingalternating-current signals obtained via the coil antenna, and a powersupply unit (33) coupled to the rectifier circuit.

The power supply unit includes a voltage step-down circuit (331) forreducing the output of the rectifier circuit, a charge control circuit(332) for charging a battery by using the output of the voltagestep-down circuit, and a communication controller power supply unit(333) for forming an operational power supply voltage of thecommunication controller on the basis of the output of the voltagestep-down circuit.

The voltage step-down circuit includes a switching regulator (200) whichcan reduce the voltage output from the rectifier circuit, and aselection circuit (206 and 208) which can select between an output pathor a first path (PT1) of the switching regulator and a bypass path or asecond path (PT2) for bypassing the switching regulator. That is, theoutput path or the first path (PT1) is used as a path for supplying theoutput voltage of the switching regulator to a communication controllerpower supply circuit (333). In contrast, the bypass path or the secondpath (PT2) is used as a path for supplying the output voltage of therectifier circuit (32) to the communication controller power supplycircuit (333) without passing through the switching regulator (200), andis used as a different path from the output path or the first path.

In other words, the output path or the first path (PT1) is a path forcoupling the output of the switching regulator to the input of thecommunication controller power supply circuit (333). The bypass path orthe second path (PT2) is a path for coupling the output of the rectifiercircuit (32) to the input of the communication controller power supplycircuit (333). The bypass path or the second path (PT2) can also couplethe output of the rectifier circuit (32) to the input of thecommunication controller power supply circuit (333) directly orindirectly via another regulator which is different from the switchingregulator.

In addition, the voltage step-down circuit includes a selection controlcircuit (207). The selection control circuit supplies voltage to thecommunication controller power supply circuit via the bypass path bycausing the selection circuit to select the bypass path at the time ofactivating the communication controller. Then, after the output voltageof the switching regulator has reached a predetermined level or hasstabilized, the selection control circuit supplies the output of theswitching regulator to the communication controller power supply circuitby causing the selection circuit to select an output path of theswitching regulator.

According to the NFC communication standard, as shown in FIG. 5, forexample, the time from when RF power rises to when the initialcommunication becomes possible has to be kept, for example, 5 ms orless. A switching regulator requires an inductor and a capacitor forobtaining a predetermined direct voltage from the switching output, withthe capacitor being charged via the inductor, and thus it takes a longtime for the output voltage to stabilize. Accordingly, activation of thecommunication controller on the basis of the output voltage of theswitching regulator makes it difficult to keep the time from when RFpower rises to when the initial communication becomes possible, forexample, 5 ms or less. In contrast to this, according to the aboveconfiguration, the selection circuit selects the bypass path at the timeof activating the communication controller, to thereby supply voltage tothe communication controller power supply circuit via the bypass path. Aswitching regulator requires an inductor and a capacitor to obtain apredetermined direct voltage from the switching output, whereas a seriesregulator is neither provided with an inductor nor a capacitor and thusit takes a shorter time to stabilize the output voltage than theswitching regulator. Therefore, selection of the bypass path by theselection circuit at the time of activating the communicationcontroller, to thereby supply voltage to the communication controllerpower supply circuit via the bypass path makes it possible to achievethe requirement of keeping the time from when RF power rises to when theinitial communication becomes possible, for example, 5 ms or less.

Selection of an output path of the switching regulator by the selectioncircuit after the output voltage of the switching regulator has reacheda predetermined level causes the output of the switching regulator to besupplied to the communication controller power supply circuit. Since aswitching operation is performed in the switching regulator, a highefficiency can be obtained with a small power loss, and thus the amountof heat generation can be reduced.

[2] In the item [1], the selection circuit can be easily constituted byincluding a first switch element (208) which can select an output pathof the switching regulator by the control of the selection controlcircuit, and a second selectable switch element (206) which can selectthe bypass path by the control of the selection control circuit.

[3] After the first switch element has transitioned from an unselectedstate to a selected state and an output path of the switching regulatorhas been selected, the selection control circuit controls the secondswitch element to be in the unselected state. Overlapping of the OFFperiods of the first switch element and the second switch element maycause power supply noise due to instantaneous interruption of thevoltage being supplied. Therefore, the selection control circuitperforms control so that, as shown in FIG. 7, the second switch element(206) is controlled to be in the unselected state (OFF state) after thefirst switch element (208) has transitioned from the unselected state(OFF state) to the selected state (ON state) and the output path of theswitching regulator has been selected. Accordingly, generation of powersupply noise can be prevented since no instantaneous interruption ofvoltage occurs.

[4] In the item [3], the communication controller can include amicrocomputer.

[5] In the item [4], a series regulator (205) can be arranged betweenthe rectifier circuit and the second switch element. The seriesregulator reduces the output voltage of the rectifier circuit to apredetermined level and outputs it, in a shorter time than the timerequired from when the output voltage of the rectifier circuit issupplied to the switching regulator to when the output voltage of theswitching regulator stabilizes. Since providing such a series regulatorallows the voltage reduced by the series regulator to be supplied to thecommunication controller power supply circuit, it is expected that theload is mitigated when further reducing the voltage in the communicationcontroller power supply circuit.

[6] In the item [4], the second switch element can be formed so as toselect the output of the rectifier circuit. In this case, it is expectedthat voltage step-down circuit can be simplified since the seriesregulator or the like is not arranged between the rectifier circuit andthe second switch element.

[7] A wireless charging system can be formed by including a powertransmitting-side device, and a power receiving-side device which canreceive power from a power transmitting-side device in the non-contactstate. In this case, the power receiving-side device can be constitutedin a manner similar to the wireless charging circuit described in theitems [1] to [6].

2. Details of Embodiments

The embodiments will be described below in more detail.

<<First Embodiment>>

FIG. 1 shows a wireless charging system.

The wireless charging system 1 shown in FIG. 1 includes a powertransmitting-side device 2 and a power receiving-side device 3. Shortdistance wireless communication according to NFC (Near FieldCommunication) is performed between the power transmitting-side device 2and the power receiving-side device 3. In addition, it is configuredsuch that power is supplied from the power transmitting-side device 2 tothe power receiving-side device 3 in a non-contact manner.

The power transmitting-side device 2 includes a modulation controlcircuit 21, a driver modulation circuit 22, a matching circuit 23, acoil antenna 24, an NFC controller 25, and an NFC power supply circuit26. The driver modulation circuit 22 modulates the carrier waveaccording to the data to be transmitted in the case of NFCcommunication, whereas it forms an unmodulated signal for power supplyin the case of power transmission. The coil antenna 24 is excited by theoutput of the driver modulation circuit 22. The modulation controlcircuit 21 controls modulation operation of the driver modulationcircuit 22. The matching circuit 23 is coupled in parallel to the coilantenna 24 to forma resonance circuit. The received signal in NFCcommunication is taken into the NFC controller 25 via the matchingcircuit 23. The NFC controller 25, which is formed by a microcomputerprovided with an NFC communication function, includes a control circuit251, a memory circuit 252, and a communication circuit 253, although notparticularly limited thereto. The control circuit 251, which is formedby CPU, executes a predetermined program for NFC control. The memorycircuit 252 includes a ROM (Read Only Memory) and a RAM (Random AccessMemory). The ROM has a program executed by the CPU stored therein. TheRAM is used for a work area of the processing performed by the CPU. Thecommunication circuit 253 performs short distance wireless communicationvia the coil antenna 24. An operational power supply of the NFCcontroller 25 is supplied from an NFC power supply circuit 26. The NFCpower supply circuit 26 is supplied with power supply voltage by a poweradapter, or a Universal Serial Bus (USB), although not particularlylimited thereto.

The power receiving-side device 3 includes the coil antenna 36, amatching circuit 31, the rectifier circuit 32, the power supply unit 33,a battery 34, and an NFC controller 35. The coil antenna 36 generateselectromotive force (alternating-current signal) by an alternatingmagnetic field generated by a coil antenna 23 of the powertransmitting-side device 2. The matching network 31 is coupled inparallel to the coil antenna 36 to forma resonance circuit. Therectifying circuit 32 rectifies the alternating-current signal obtainedvia the coil antenna 36. The power supply unit 33 supplies theoperational power supply voltage to an electronic circuit EC which isassumed to be a load circuit of a smart phone or the like, suppliescharge voltage to the battery 34, supplies the operational power supplyvoltage to the NFC controller 35 on the basis of the output voltage ofthe rectifier circuit 32. The battery 34 is assumed to be a single cellbattery (4 to 4.2 V), for example, a lithium ion battery, although notparticularly limited thereto. The power supply unit 33 includes thevoltage step-down circuit 331, the charge control circuit 332, and theNFC power supply circuit 333. The voltage step-down circuit 331 reducesthe output voltage of the rectifier circuit 32. The charge controlcircuit 332 charges the battery 34 on the basis of the output voltage ofthe voltage step-down circuit 331. The NFC power supply circuit 333generates the operational power supply voltage of the NFC controller 35.The received signal in NFC communication is taken into the NFCcontroller 35 via the matching circuit 31. The NFC controller 35, whichis formed with a microcomputer, includes a communication circuit 351, amemory circuit 352, and a control circuit 353, although not particularlylimited thereto. The communication circuit 351 performs short distancewireless communication via the coil antenna 36. The control circuit 353,which is formed with a CPU, executes a predetermined program for NFCcontrol. The memory circuit 352 includes a ROM and a RAM. The ROM has aprogram executed by the CPU stored therein. The RAM is used for a workarea of the processing performed by the CPU.

FIG. 2 shows an exemplary configuration of the power supply unit 33 indetail. The power supply unit 33 is assumed to be a semiconductor devicein the form of a resin package sealed by insulative resin such as moldresin, although not particularly limited thereto.

The main part of the power supply unit 33 shown in FIG. 2, which isformed over a single semiconductor substrate such as a silicon substrateby known semiconductor integrated circuit manufacturing technology,although not particularly limited thereto, will be referred to as a“power supply chip”. The power supply chip 33C includes the voltagestep-down circuit 331, the charge control circuit 332, an analog-digitalconverter (abbreviated as “ADC” in the following) 210, a pull-up powersupply circuit 211, and the NFC power supply circuit 333.

The power supply chip 33C has provided therein a power supply inputterminal VIN, a ground terminal DDGND, output terminals DDOUT1 andDDOUT2, a system power supply output terminal SYS, a charging terminalRICHG, a battery coupling terminal BAT, a battery voltage terminal VBAT,a thermistor coupling terminal TH, and a thermistor power supplyterminal THVDD. In addition, the power supply chip 33C has providedtherein NFC power supply output terminals VDD1 and VDD2, an input/outputterminal IO, and a serial interface terminal SIF. The output voltage ofthe rectifier circuit 32 is input via the power supply input terminalVIN. The ground terminal DDGND is assumed to be a ground terminal of aswitching regulator 200. The output terminals DDOUT1 and DDOUT2 have aninductor 202 and a capacitor 203 externally attached thereto. The systempower supply output terminal SYS is coupled to, for example, anelectronic circuit such as a smart phone, and thus power is supplied tothe electronic circuit via the system power supply output terminal SYS.The charging terminal RICHG has a resistor 212 externally attachedthereto. The maximum current value for battery charging is determined bythe value of the resistor 212. The battery coupling terminal BAT and thebattery voltage terminal VBAT have the positive electrode terminal (+)of the battery 34 coupled thereto. The thermistor coupling terminal THhas the Terminal T of thermistor 214 coupled thereto. The thermistor 214is arranged in the vicinity of the battery 34 for detecting thetemperature of the battery 34. The thermistor power supply terminalTHVDD has thermistor 214 coupled thereto via the resistor 213. Theoperational power supply voltage of the NFC controller 35 is output fromthe NFC power supply output terminals VDD1 and VDD2. Various controlinformation is allowed to be input and output via the input/outputterminal IO or the serial interface terminal SIF. That is, theinput/output terminal IO and the serial interface terminal SIF areallowed to be coupled to the NFC controller 35, and used to input andoutput various control information between the power supply unit 33 andthe NFC controller 35.

The voltage step-down circuit 331 reduces the voltage which has beentaken in from the rectifier circuit 32 via the power supply inputterminal VIN. The output voltage of the voltage step-down circuit 331 istransmitted to the charge control circuit 332, the ADC210, the pull-uppower supply circuit 211, and the NFC power supply circuit 333. Inaddition, the output voltage of the voltage step-down circuit 331 andthe output voltage of the battery 34 are allowed to be externally outputvia the system power supply output terminal SYS.

The charge control circuit 332 charges the battery 34 via the chargingterminal RICHG and the battery coupling terminal BAT. In addition, theoutput voltage of the battery 34 is assumed to be transmittable to thesystem power supply output terminal SYS via the charge control circuit332.

The ADC210 takes in the output voltage of the battery 34 via the batteryvoltage terminal VBAT, and converts it into digital data. In addition,the ADC210 takes in the result of temperature detection by thermistor214 via thermistor coupling terminal TH, and converts it into digitaldata. The digital signal output of the ADC210 is transmitted by a logiccircuit within the voltage step-down circuit 331.

The pull-up power supply circuit 211 supplies the pull-up power supplyvoltage to thermistor 214 via thermistor power supply terminal THVDD andthe resistor 213.

The NFC power supply circuit 333 generates the operational power supplyvoltage of the NFC controller 35 on the basis of the output of thevoltage step-down circuit 331. The output voltage of the NFC powersupply circuit 333 is supplied to the NFC controller 35 via the NFCpower supply output terminals VDD1 and VDD2. In this example, it isassumed, in relation with the microcomputer applied to the NFCcontroller 35, that 3.0 V is output via the NFC power supply outputterminal VDD1 and 1.8 V is output via the NFC power supply outputterminal VDD2, although not particularly limited thereto.

The voltage step-down circuit 331 includes the switching regulator(DC-DC converter) 200, a current limiting element 204, the switchelements 206 and 208, the series regulator 205, the selection controlcircuit 207, and a logic circuit 209.

The switching regulator 200, which includes a switching circuit 201, theinductor 202, the capacitor 203, reduces the output voltage of therectifier circuit 32.

The switching circuit 201 takes out the required energy by switchingfrom the voltage which has been input via the power supply inputterminal VIN. The output of the switching circuit 201 is supplied to theinductor 202 and the capacitor 203, and thus a direct voltage at apredetermined level is formed. The switching circuit 201 can beconstituted by including, as shown in FIG. 3 for example, a switchelement 401, a diode 402, an error amplifier 403, a reference voltagesupply 404, and a PWM (pulse width modulation) comparator 405. The erroramplifier 403 amplifies the difference between the reference voltage ofthe reference voltage supply 404 and the voltage of the output terminalDDOUT2. The output of the error amplifier 403 is transmitted to the PWMcomparator 405. The PWM comparator 405 compares the output of the erroramplifier 403 with an internally generated sawtooth wave, to therebyform a PWM signal. The switching operation of the switch element 401 iscontrolled by the formed PWM signal. The diode 402 is provided in orderto maintain the current supply to the inductor 202 during the OFF periodof the switch element 401. The switch element 401 can have a p-channelMOS transistor applied thereto. In addition, the diode 402 can bereplaced with an n-channel MNOS transistor controlled by the PWMcomparator.

The current limiting element 204 in FIG. 2 is provided in order to limitthe output current of the switching regulator 200 in order to protectthe switching regulator 200. The output of the switching regulator 200is transmitted to the charge control circuit 332 and the system powersupply output terminal SYS or the like, via the current limiting element204. The current limiting element 204 can have a p-channel MOStransistor applied thereto.

The switch element 208 is provided in order to select a path (outputpath (or first path) of the switching regulator) PT1 through which theoutput voltage of the switching regulator 200 is transmitted to the NFCpower supply circuit 333. The switch element 206 is provided in order toselect a bypass path (or second path) PT2 for bypassing the switchingregulator 200. That is, the bypass path (or second path) PT2 is assumedto be path for transmitting the output voltage of the rectifier circuit32 to the NFC power supply circuit 333 via the series regulator 205,without going through the switching regulator 200, and assumed to be adifferent path from the output path (or first path) PT1. In other words,the output path or first path (PT1) is a path for coupling the output ofthe switching regulator 200 to the input of the NFC power supply circuit333. The bypass path (or second path) PT2 is a path for coupling theoutput of the rectifier circuit 32 to the input of the NFC power supplycircuit 333. The bypass path (or second path) PT2 couples the output ofthe rectifier circuit 32 to the input of the NFC power supply circuit333, via another regulator (series regulator 205) which is differentfrom the switching regulator 200.

The switch elements 206 and 208 function as a selection circuit whichcan select the output path PT1 of the switching regulator 200 and thebypass path PT2. The switch elements 206 and 208 can have a p-channelMOS transistor applied thereto.

The selection operation of the switch elements 206 and 208 is controlledby the selection control circuit 207. The selection control circuit 207couples the bypass path PT2 to the NFC power supply circuit 333 bycausing the switch element 206 to select the bypass path PT2 at the timeof activating the NFC controller 35. In addition, after the outputvoltage of the switching regulator 200 has reached a predetermined levelor stabilized, the selection control circuit 207 supplies the output ofthe switching regulator 200 to the NFC power supply circuit 333 bycausing the switch element 208 to select the output path PT1 of theswitching regulator 200. The selection control circuit 207, as shown inFIG. 6, is constituted by including a comparator 602 which comparesoutput of the switching regulator 200 with the reference voltage of areference voltage supply 601, and a controller 603 for controlling theselection operation of the switch elements 206 and 208 on the basis ofthe result of comparison by the comparator 602. Basically, the switchelements 206 and 208 are switched on and off complementarily by thecontroller 603. That is, if switching on the switch element 206 causesthe output of the series regulator 205 to be supplied to the pull-uppower supply circuit 211 and the NFC power supply circuit 333, theswitch element 208 is switched off. If, in contrast, switching on theswitch element 208 causes the output of the switching regulator 200 tobe supplied to the pull-up power supply circuit 211 and the NFC powersupply circuit 333, the switch element 206 is switched off. If the OFFperiods of the switch elements 206 and 208 overlap in such switching,power supply noise may occur due to instantaneous interruption of thevoltage supplied to the pull-up power supply circuit 211 and the NFCpower supply circuit 333. Therefore, the selection control circuit 207performs control so that, as shown in FIG. 7, the switch element 206 iscontrolled in the unselected state (OFF state), after the switch element208 has transitioned from the unselected state (OFF state) to theselected state (ON state) and the output path PT1 of the switchingregulator 200 has been selected. That is, by providing an overlap period701 during which the switch elements 206 and 208 are both in the ONstate, instantaneous interruption of the voltage supplied to the pull-uppower supply circuit 211 and the NFC power supply circuit 333 isavoided, and generation of power supply noise is prevented.

The series regulator 205 in FIG. 2 is arranged between the rectifiercircuit 32 and the switch element 206. The series regulator 205 reducesthe output voltage of the rectifier circuit 32 to a predetermined leveland outputs it, in a shorter time than the time required from when theoutput voltage of the rectifier circuit 32 is supplied to the switchingregulator 200 to when the output voltage of the switching regulator 200stabilizes. A low-dropout (abbreviated as “LDO”) regulator, for example,as shown in FIG. 4 can be applied to the series regulator 205. The LDOregulator shown in FIG. 4 is constituted by including a voltage supply301, an error amplifier 302, a p-channel MOS transistor 303, andresistors 304 and 305. The p-channel MOS transistor 303 is provided overthe bypass path PT2. A voltage at the output of the p-channel MOStransistor 303 is detected by a series coupling circuit of the resistors304 and 305, the difference between the detection result and thereference voltage of the reference voltage supply 301 is amplified bythe error amplifier 302, and the ON resistance value of the p-channelMOS transistor 303 is controlled by the output of the error amplifier302. With such a control, the p-channel MOS transistor 303 reduces theinput voltage of the series regulator 205.

In the NFC power supply circuit 333, two types of output voltages,namely 3.0 V and 1.8 V, can be generated by providing two units of LDOregulators as shown in FIG. 4.

The logic circuit 209 in FIG. 2 includes registers for various controls,and performs various condition settings for the charge control circuit332 with regard to battery charging, according to input clock signals.The clock signals are generated inside or outside the power supply chip33C. The logic circuit 209 is coupled to the NFC controller 35 via theserial interface terminal SIF or the input/output terminal IO andexchanges various control information with the NFC controller 35. Inaddition, the charging status of the battery 34 is transmitted from thecharge control circuit 332 to logic circuit 209 by a charging statussignal CSS. The logic circuit 209 sets 332 condition information PI withregard to battery charging for the charge control circuit, on the basisof the temperature detection result in the chip, and the output of theADC210 (terminal voltage information of the battery 34, and temperatureinformation of the battery 34) DO. Battery charging is performed by thecharge control circuit 332 according to the setting. The operationalpower supply voltage of the logic circuit 209 can be generated by adifferent regulator from the switching regulator 200 and the seriesregulator 205, on the basis of the voltage which has been input via thepower supply input terminal VIN.

When the coil antenna 24 in the power transmitting-side device 2 isapproached by a coil antenna in the power receiving-side device 3 in theconfiguration described above, initial communication (NFC communication)is performed between the power transmitting-side device 2 and the powerreceiving-side device 3 to exchange information such as whether or notthe target of charging is an authenticated device, or information aboutlink status or required power for charging. On the basis of theinformation exchanged by the initial communication, setting ofrespective units is performed in the power transmitting-side device 2and the power receiving-side device 3. According to the NFCcommunication standard, as shown in FIG. 5, for example, the time fromwhen RF power rises to when the initial communication becomes possible,has to be kept, for example, 5 ms or less.

In the switching regulator 200, the inductor 202 and the capacitor 203are indispensable to obtain a predetermined direct voltage becauseswitching is performed by the p-channel MOS transistor 401 on the basisof the output of the PWM comparator 405, with the capacitor 203 beingcharged via the inductor 202, and therefore it takes awhile for theoutput voltage to stabilize. Accordingly, activation of the NFCcommunication controller 35 on the basis of the output voltage of theswitching regulator 200 makes it difficult to keep the time from when RFpower in the power receiving-side device 3 rises to when the initialcommunication becomes possible, for example, 5 ms or less.

According to configuration shown in FIG. 2, however, when a voltageinduced in the coil antenna 36 in the power receiving-side device 3 isrectified by the rectifier circuit 32 and transmitted to the seriesregulator 205, the voltage is reduced by the series regulator 205 andthe output of the series regulator 205 is supplied to the NFC powersupply circuit 333 via the switch element 206. The LDO regulator such asthat shown in FIG. 4 is neither provided with the inductor 202 nor thecapacitor 203, and thus it takes a shorter time to stabilize the outputvoltage than the switching regulator 200. Therefore, supply of theoutput of the switching regulator 200 to the NFC power supply circuit333 and activation of the NFC controller 35 by the output of the NFCpower supply circuit 333 on that occasion make it possible to achievethe requirement of keeping the time from when RF power rises to when theinitial communication becomes possible, for example, 5 ms or less.

In contrast, since the consumption current is relatively small when theinitial communication (NFC communication) is performed in the NFCcontroller 35, the Joule heat which occurs in the p-channel MOStransistor 303 in the series regulator 205 can be tolerated. However, acase is possible where consumption current becomes large depending onthe operation mode other than the initial communication (NFCcommunication) in the NFC controller 35, in which case the Joule heatwhich occurs in the p-channel MOS transistor 303 in the series regulator205 can no longer be tolerated.

According to configuration shown in FIG. 2, therefore, the output of theswitching regulator 200 is supplied to the NFC power supply circuit 333by causing the switch element 208 to select the output path PT1 of theswitching regulator 200 after the output voltage of the switchingregulator 200 reached a predetermined level. Since starting the supplyof the output of the switching regulator 200 to the NFC power supplycircuit 333 causes the switch element 206 to be switched off by theselection control circuit 207, the output of the series regulator 205will no longer be consumed. Since a switching operation is performed inthe switching regulator 200, a high efficiency can be obtained with asmall power loss, where the amount of heat generation is small incomparison with the LDO regulator.

After the initial communication (NFC communication) has been performedbetween the power transmitting-side device and the power receiving-sidedevice 3 to exchange information such as whether or not the target ofcharging is an authenticated device, or information about link status orrequired power for charging and, on the basis of the informationexchanged by the initial communication, setting of respective units hasbeen performed in the power transmitting-side device 2 and the powerreceiving-side device 3, charging of the battery 34 is started by thecontrol of the charge control circuit 332. The terminal voltage of thebattery 34 is monitored by the logic circuit 209 via the ADC210. Whenthe terminal voltage of the battery 34 reaches a predetermined level,wireless battery charging is finished. In addition, battery charging isinterrupted if the power receiving-side device 3 moves away from thepower transmitting-side device 2 and NFC communication can no longer benormally performed.

<<Second Embodiment>>

Although the series regulator 205 is arranged between the power supplyinput terminal VIN and the switch element 206 in the first embodiment asshown in FIG. 2, the series regulator 205 may be omitted and the switchelement 206 may be coupled to the power supply input terminal VIN.According to such a configuration, omitting the series regulator 205causes the voltage transmitted from the rectifier circuit 32 to thepower supply input terminal VIN to be supplied to the pull-up powersupply circuit 211 and the NFC power supply circuit 333 via the switchelement 206. The voltage transmitted from the rectifier circuit 32 tothe power supply input terminal VIN, being several dozen Volts, issupposed to be supplied to the pull-up power supply circuit 211 and theNFC power supply circuit 333, and thus the load of reducing the voltagein the pull-up power supply circuit 211 and the NFC power supply circuit333 grows larger. However, the circuit size of the voltage step-downcircuit 331 is reduced in comparison with the case shown in FIG. 2 byomitting the series regulator 205.

Although the present invention has been specifically described above onthe basis of embodiments, it is needless to say that the invention isnot limited to the embodiments and can be modified in various ways in arange not deviating from its concept.

For example, the power supply unit 33 and the NFC controller 35 may beformed in a single IC.

What is claimed is:
 1. A wireless communication device comprising: acommunication control circuit configured to transmit and receive controlinformation; a power control circuit including a first regulatorcircuit, a second regulator circuit and a selection circuit, the powercontrol circuit being configured to receive a source voltage, supply apower supply voltage to the communication control circuit and output acharging voltage to a battery, the first regulator circuit beingconfigured to input the source voltage and output a first voltage to theselection circuit; the second regulator circuit being configured toinput the source voltage and output a second voltage to the selectioncircuit; wherein the selection circuit is configured to select andoutput the first voltage as the power supply voltage when a level of thefirst voltage reaches a predetermined level, and to select and outputthe second voltage as the power supply voltage when the level of thefirst voltage has not reached the predetermined level, wherein anactivation time of the second regulator is faster than that of the firstregulator, wherein the first regulator circuit includes a switchingregulator, and wherein the second regulator circuit includes a seriesregulator.
 2. A wireless communication device according to claim 1, apower consumption of the first regulator is smaller than that of thesecond regulator.
 3. A wireless communication device according to claim1, wherein the selection circuit further includes a comparator circuitand a selection circuit, wherein the comparator circuit is configured tocompare the first voltage with a reference voltage and output a resultvoltage to the selection control circuit, wherein the selection controlcircuit is configured to select the power supply voltage from the firstvoltage and the second voltage based on the result voltage.
 4. Awireless communication device according to claim 3, wherein the controlinformation includes a state of wireless communication.
 5. A wirelesscommunication device according to claim 1, further comprising: a coilantenna; a rectifier circuit configured to couple with the coil antenna,the rectifier circuit being configured to rectify an alternating-currentsignal obtained via the coil antenna and output the source voltage tothe power control circuit.